Distributed sensor networks use a set of spatially scattered sensors designed to obtain measurements from the environment. A central node connected to the sensors collects the data, which is used to extract relevant information about the environment.
Conventional network types, such as the RS-485 network, allow the implementation of linear bus topologies (e.g., in-line serial drop communication links). However, such networks have bandwidth/data rate limitations that constrain the quantity of and the physical spacing between sensors employed. Data rates (baud rates) are typically governed by cable length and physical signaling protocols. Electrical cables have an inherent low-pass filtration characteristic (due to intrinsic inductance, resistance, and capacitance), which leads to lower data rates for longer spans of the electrical cable. Data protocols attempt to optimize signal integrity and may limit the bit error rate for a given design parameter. Extending length and number of distributed sensors may require additional busses or cables running at slower baud rates. Manufacturability may become increasingly more expensive as additional cables are added to accommodate sensor bandwidth, which can lead to solutions that may not be realistic in terms of cost.
Some semiconductor manufacturers have developed RS-485 transceiver devices with built-in cable equalization (e.g., high-frequency gain circuits) that extends the range of an RS-485 network. While these devices may succeed in lengthening the range of such networks, they still have a limit to their maximum range. Further, these devices do not attempt to address the concept of synchronization.
Other network types such as Ethernet and USB have existing methods for extending their range; however, these methods often impose high power consumption, cost, and even size making them unsuitable for many applications, such as long-distance sub-sea surveillance.
What is desired is an extendable synchronous low power telemetry system for distributed sensor networks that is low cost, reliable, and readily scalable.